Abstract: [Objective]It is crucial to clarify the seepage law of granite colluvial soil for engineering construction, agricultural activities, ecological restoration and geological disaster prevention in the area. [Methods] In this paper, the constant head permeability tests of granite colluvial soil under different initial dry densities are carried out, and the seepage characteristics of granite colluvial soil under low hydraulic gradient are studied. [Results] The results indicate that granite colluvial soil have different degrees of fluctuation characteristics under low hydraulic gradient. The permeability coefficient increases with the hydraulic gradient under all dry density conditions. When the hydraulic gradient reaches the critical hydraulic gradient icr, the permeability coefficient remains basically unchanged, and the permeability coefficient at this moment decreases logarithmically with the increase of dry density. And the critical hydraulic gradient of the transition fluctuates greatly under low dry density conditions. While the dry density is greater than 1.5g / cm3, the critical hydraulic gradient icr increases linearly with the dry density. [Conclusion] The saturated seepage of granite residual soil under different dry density conditions has fluctuation characteristics under low hydraulic gradient. Then, the prediction equations of critical hydraulic gradient and permeability coefficient in the linear seepage stage of granite colluvial soil under different dry density conditions are clarified. Combined with pore seepage theory, the reasons of fluctuation seepage and its transformation of granite colluvial soil under low hydraulic gradient is preliminarily discussed. The research results provide a new viewpoint for the study of seepage process of granite colluvial soil and provide a reference for consolidation analysis and seepage stability calculation of granite colluvial soil.